1. Field of the Invention
This invention relates to retractable landing gear for aircraft, and in particular to a float retractable landing gear.
2. Background of the Invention
Before the Wright brothers made their famous “first flight” on Dec. 12, 1903, another aviator named Samuel P. Langley attempted two powered flights launched from a houseboat in his Langley Aerodrome. These attempts occurred on Oct. 7 and Dec. 8, 1903. Unfortunately, both ended in premature water landings in the Potomac River.
Sadly, Langley died in 1906 without again attempting flight. The Langley Aerodrome was consigned to storage, where it languished until 1914. During that year the Smithsonian Institute sponsored a study of its airworthiness. The Aerodrome was taken out of storage and shipped to the Curtiss factory at Hammonsport. Glenn Curtiss undertook its restoration, and made several modifications, including mounting it on floats.
During the morning of May 29, 1914 Curtiss flew the Aerodrome 150 feet, and landed softly on the water. This was accomplished despite the addition of 350 pounds of weight, caused by the floats and their supports. Thus, it could be argued that the first aircraft design capable of engaging in controlled, powered flight, was a seaplane!
Seaplanes acquired great utility in the years before World War II, when few land airports existed. Seaplanes, as opposed to land planes, could alight anywhere suitable smooth water existed. The large flying boats of the era plied the airways from Europe to Africa, around the Americas and across the Pacific to the Far East.
Seaplanes still enjoy popularity in areas lacking land airports, such as Canada and Alaska. In addition, the sheer joy of landing and taking off from water attracts innumerable aficionados, who fly a wide variety of seaplanes.
Seaplanes are classified as flying boats or floatplanes. Flying boats land on their bellies in the water, and typically incorporate small floats called sponsons on their wings for roll stability while on the water. Float planes, on the other hand, typically feature a pair of large, parallel sausage-shaped floats attached to their undersides by struts. Floatplanes are generally high-wing, and thus easier to dock than flying boats, because their wings don't interfere with the dock. The float plane design also provides the flexibility of being able to mount floats on existing land plane designs. This flexibility saves time and money, because an entirely new airplane need not be designed—merely a means of attaching floats to an existing design.
Floatplanes may be equipped with retractable wheels, or landing gear, so as to afford the added versatility of being able to land on water or on a land runway. This type of floatplane is called an amphibian. Amphibians truly have the best of all worlds: they can land on any suitable land runway, and in addition they can land on any suitable water surface. This versatility permits a float plane to take off from a city airport, and land at its owner's lake out in the country. Amphibious floatplanes are commonly used to provision lake-side hunting and fishing camps, remote villages, and to transport patients from remote locations to hospitals.
An amphibian pilot must always be certain to have the retractable landing gear in the correct position when landing. Student floatplane pilots are taught to recite the mantras: “This is a LAND landing—gear checked DOWN” and “This is a WATER landing—gear checked UP”. Making a land landing with the retractable landing gear erroneously retracted generally doesn't seriously damage the floats (although the runway surface could scrape them up some), or injure the floatplane occupants.
Making a water landing with the gear erroneously extended, however, is a horse of a different color. Landing in the water with gear extended could destroy the aircraft and seriously injure or kill its occupants. The reason is that on initial contact during landing, the floats are supposed to skim across the water on plane like water skis. As more weight put on the floats, the floatplane is supposed to gradually slow down without capsizing, until settling into displacement, where the entire aircraft weight is supported by the buoyancy of the floats.
If a floatplane's landing gear is in the extended position on initial contact with the water, the wheels tend to dig into the water, and slow the aircraft too quickly. This abrupt deceleration could hurl the aircraft over onto its nose, and the aircraft could literally dive nose first into the water. The abrupt stop could injure the occupants. In addition, an aircraft suddenly turned submarine, or floating inverted on its back in the water with its cabin submerged, poses significant drowning hazard.
Landing gear which retracts into a float is typically protected by gear doors which close after the gear has retracted. In land planes gear doors are installed to reduce drag, and therefore increase aircraft performance, principally speed aloft. In amphibians a more important reason for gear doors exists: to prevent water from entering the wheel well during water landings.
A typical float plane may land at 60 MPH. If the gear doors are open at that speed when the float initially contacts water, the wheel wells will immediately fill with water at high pressure urged into the wells by virtue of the speed of the airplane relative to the water. At high impact speeds water becomes a formidable force. Water landings with open gear doors have been known to result in the hull tearing open due to water pressure, hastening the airplane's sinking and the risk of occupant drowning and injury.
Even where the landing gear is correctly retracted during a water landing, if the gear doors should fail open, a similar result to a gear-down water landing may obtain: hull damage and sinking of the aircraft, with attendant hazard to its occupants. Thus, it would be desirable to provide a gear design incorporating gear doors which are sturdy and resistant to failure in the presence of water pressure during a water landing.
Existing Designs
A number float retractable landing gear designs have been proposed. One design provides main landing gear which retracts rear-wards into the floats aft of the float step. The nose gear extends from the nose of the aircraft. Many light and ultra-light aircraft designs incorporate a high-wing mounted engine driving a pusher propeller, so the nose of such aircraft doesn't contain any structural re-enforcement (which it would if the engine were nose-mounted) onto which to attach the retractable nose gear. This re-enforcement must be added, increasing the aircraft weight and nose gear loading.
Another approach is to provide a pair of opposing gear doors mounted to the bottom of the float forward of the step. The hydrodynamic forces exerted on the float during water landings subjects these gear doors to high stresses, which may contribute to their failure. As noted above, gear door failure during water landings can have dire consequences, indeed.